Example Converter File xlsx to csv

var
apppath : string;
procedure Form1_Button1_OnClick (Sender: TObject; var Cancel: boolean);
var
ExcelFile : Variant;
WorkBook  : Variant;
WorkSheet : Variant;
begin
    ExcelFile :=  CreateOleObject('Excel.Application');
    WorkBook  :=  ExcelFile.WorkBooks.Open(apppath+'xxx.xlsx');
    WorkSheet :=  WorkBook.WorkSheets.Item['Sheet1'];
    WorkBook.SaveAs(apppath+'xxx.xlsx'+'.csv', 62) ;
    WorkBook.Close;
    ExcelFile.Quit;
end;
begin
    apppath := ExtractFilePath(Application.ExeName);
end.

// XlFileFormat enumeration (Excel)
// https://docs.microsoft.com/en-us/office/vba/api/excel.xlfileformat
// | Name                              | Value     | Description                               | Extension                |
// | :-------------------------------- | :-------- | :---------------------------------------- | :----------------------- |
// | **xlAddIn**                       | 18        | Microsoft Excel 97-2003 Add-In            | *.xla                    |
// | **xlAddIn8**                      | 18        | Microsoft Excel 97-2003 Add-In            | *.xla                    |
// | **xlCSV**                         | 6         | CSV                                       | *.csv                    |
// | **xlCSVMac**                      | 22        | Macintosh CSV                             | *.csv                    |
// | **xlCSVMSDOS**                    | 24        | MSDOS CSV                                 | *.csv                    |
// | **xlCSVUTF8**                     | 62        | UTF8 CSV                                  | *.csv                    |
// | **xlCSVWindows**                  | 23        | Windows CSV                               | *.csv                    |
// | **xlCurrentPlatformText**         | -4158     | Current Platform Text                     | *.txt                    |
// | **xlDBF2**                        | 7         | Dbase 2 format                            | *.dbf                    |
// | **xlDBF3**                        | 8         | Dbase 3 format                            | *.dbf                    |
// | **xlDBF4**                        | 11        | Dbase 4 format                            | *.dbf                    |
// | **xlDIF**                         | 9         | Data Interchange format                   | *.dif                    |
// | **xlExcel12**                     | 50        | Excel Binary Workbook                     | *.xlsb                   |
// | **xlExcel2**                      | 16        | Excel version 2.0 (1987)                  | *.xls                    |
// | **xlExcel2FarEast**               | 27        | Excel version 2.0 far east (1987)         | *.xls                    |
// | **xlExcel3**                      | 29        | Excel version 3.0 (1990)                  | *.xls                    |
// | **xlExcel4**                      | 33        | Excel version 4.0 (1992)                  | *.xls                    |
// | **xlExcel4Workbook**              | 35        | Excel version 4.0. Workbook format (1992) | *.xlw                    |
// | **xlExcel5**                      | 39        | Excel version 5.0 (1994)                  | *.xls                    |
// | **xlExcel7**                      | 39        | Excel 95 (version 7.0)                    | *.xls                    |
// | **xlExcel8**                      | 56        | Excel 97-2003 Workbook                    | *.xls                    |
// | **xlExcel9795**                   | 43        | Excel version 95 and 97                   | *.xls                    |
// | **xlHtml**                        | 44        | HTML format                               | *.htm; *.html            |
// | **xlIntlAddIn**                   | 26        | International Add-In                      | No file extension        |
// | **xlIntlMacro**                   | 25        | International Macro                       | No file extension        |
// | **xlOpenDocumentSpreadsheet**     | 60        | OpenDocument Spreadsheet                  | *.ods                    |
// | **xlOpenXMLAddIn**                | 55        | Open XML Add-In                           | *.xlam                   |
// | **xlOpenXMLStrictWorkbook**       | 61 (&H3D) | Strict Open XML file                      | *.xlsx                   |
// | **xlOpenXMLTemplate**             | 54        | Open XML Template                         | *.xltx                   |
// | **xlOpenXMLTemplateMacroEnabled** | 53        | Open XML Template Macro Enabled           | *.xltm                   |
// | **xlOpenXMLWorkbook**             | 51        | Open XML Workbook                         | *.xlsx                   |
// | **xlOpenXMLWorkbookMacroEnabled** | 52        | Open XML Workbook Macro Enabled           | *.xlsm                   |
// | **xlSYLK**                        | 2         | Symbolic Link format                      | *.slk                    |
// | **xlTemplate**                    | 17        | Excel Template format                     | *.xlt                    |
// | **xlTemplate8**                   | 17        | Template 8                                | *.xlt                    |
// | **xlTextMac**                     | 19        | Macintosh Text                            | *.txt                    |
// | **xlTextMSDOS**                   | 21        | MSDOS Text                                | *.txt                    |
// | **xlTextPrinter**                 | 36        | Printer Text                              | *.prn                    |
// | **xlTextWindows**                 | 20        | Windows Text                              | *.txt                    |
// | **xlUnicodeText**                 | 42        | Unicode Text                              | No file extension; *.txt |
// | **xlWebArchive**                  | 45        | Web Archive                               | *.mht; *.mhtml           |
// | **xlWJ2WD1**                      | 14        | Japanese 1-2-3                            | *.wj2                    |
// | **xlWJ3**                         | 40        | Japanese 1-2-3                            | *.wj3                    |
// | **xlWJ3FJ3**                      | 41        | Japanese 1-2-3 format                     | *.wj3                    |
// | **xlWK1**                         | 5         | Lotus 1-2-3 format                        | *.wk1                    |
// | **xlWK1ALL**                      | 31        | Lotus 1-2-3 format                        | *.wk1                    |
// | **xlWK1FMT**                      | 30        | Lotus 1-2-3 format                        | *.wk1                    |
// | **xlWK3**                         | 15        | Lotus 1-2-3 format                        | *.wk3                    |
// | **xlWK3FM3**                      | 32        | Lotus 1-2-3 format                        | *.wk3                    |
// | **xlWK4**                         | 38        | Lotus 1-2-3 format                        | *.wk4                    |
// | **xlWKS**                         | 4         | Lotus 1-2-3 format                        | *.wks                    |
// | **xlWorkbookDefault**             | 51        | Workbook default                          | *.xlsx                   |
// | **xlWorkbookNormal**              | -4143     | Workbook normal                           | *.xls                    |
// | **xlWorks2FarEast**               | 28        | Microsoft Works 2.0 far east format       | *.wks                    |
// | **xlWQ1**                         | 34        | Quattro Pro format                        | *.wq1                    |
// | **xlXMLSpreadsheet**              | 46        | XML Spreadsheet                           | *.xml                    |